This invention is related to a catalyst for the conversion of hydrocarbons which catalyzes the reaction of hydrogen with organic-sulfur and organic-nitrogen compounds. In particular, the invention relates to a catalyst for hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) of distillates of petroleum, such as vacuum distillates, atmospheric distillates, diesel fuel, kerosene, and gasolines, with high catalytic activity and stability. More particularly, the present invention relates in its preferred embodiment to a cobalt-molybdenum catalyst supported by an aluminum phosphate or aluminum borate useful in the hydrotreatment of distillates of petroleum, and a method for the preparation of same. The catalyst has a lower cobalt content than the previous state-of-the-art catalysts, but is competitive with them in terms of activity and stability.
Petroleum refining makes use of catalysts with special properties to stimulate the HDS and HDN reactions, by placing the catalyst in contact with hydrogen and charges of vacuum gas oils under specific conditions of temperature and pressure. In that way, the organic-sulfur and organic-nitrogen compounds are converted to hydrogen sulfide and ammonia, which are eliminated, and a product of much higher commercial value is obtained.
Many patents have been issued in recent years, making claims for compositions for differing catalysts and conditions of processing which result in the HDS and HDN of distillates of petroleum origin. These catalytic compositions make it possible to obtain acceptable operating cycles and products with low sulfur and nitrogen content. In this sense, catalysts containing specific combinations of metals selected from the VIB and VIII Groups of the Periodic Table, with and without phosphorus, have been claimed in numerous patents corresponding to the pre-existing state of the art. In particular, U.S. Pat. Nos. 3,649,523, 3,749,663, 3,755,150, 3,755,196, 3,840,472, 4,306,965, 4,382,854, 4,389,304 4,396,500 and 4,520,128 are related to the foregoing.
In general, the composition of the catalysts claimed in those patents is of the CoMo-Al.sub.2 O.sub.3 and the NiMo-Al.sub.2 O.sub.3 types, containing from 1% to 10% by weight of oxides of cobalt or nickel and from 10% to 30% by weight of molybdenum oxide supported by alumina. In addition, the formulations of the CoMoP-Al.sub.2 O.sub.3 and NiMoP-Al.sub.2 O.sub.3 types have high concentrations of metal oxides, similar to those of catalysts without phosphate, and they show special relationships with P/MoO.sub.3 of between 0.1 and 0.25, or stoichiometric relationships of P/Mo=1.0, with the aim of increasing the catalytic activity in HDS and HDN in the said catalysts. The phosphorus is generally used to stabilize the cobalt-molybdenum or the nickel-molybdenum solutions and to permit the deposition of the metals on the support base in a single step. This reduces costs involved in the preparation of the catalyst as compared with the two-step sequential processes of impregnation.
It is well known in the field that, in the preparation of the CoMo-Al.sub.2 O.sub.3 catalyst, the cobalt acts as a promoter of the HDS reaction. Nevertheless, it is necessary to add large concentrations of cobalt, since a part of that metal migrates to the alumina grid, forming a spinel of the CoAl.sub.2 O.sub.4 type, which is well known in the field. This compound is inactive in HDS, as a result of which, a large part of the cobalt thus deposited is lost. Generally, this cobalt spinel is detected in the state-of-the-art catalysts through spectroscopic analysis such as the Diffuse Reflectance Spectroscopy technique, which permits the visualization of the triplet of bands characteristic of the compound indicated above, located at 625, 590, and 550 mm.